The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0dd889e0cb36c81e872ffc768e471cb52a7f16f6

commit 0dd889e0cb36c81e872ffc768e471cb52a7f16f6
Author: Joy Ming <jming@chromium.org>
Date: Tue Aug 08 21:02:50 2017

Build fake DownloadService for testing.

As the DownloadService is becoming available to for different
components, it is important to provide a TestDownloadService that they
can use for their testing purposes. For example, OfflinePrefetch
currently has implemented their own version of a TestDownloadService.
This implementation draws inspiration from the functionality available
in that version, while also providing a shared implementation for
future components to use and extend.

Bug:  736231 
Change-Id: I87358ce54ca8055e788df9bf3877dbd9d9b3385a
Reviewed-on: https://chromium-review.googlesource.com/567585
Commit-Queue: Joy Ming <jming@chromium.org>
Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Reviewed-by: Xing Liu <xingliu@chromium.org>
Reviewed-by: Jian Li <jianli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#492750}
[modify] https://crrev.com/0dd889e0cb36c81e872ffc768e471cb52a7f16f6/components/download/internal/test/BUILD.gn
[add] https://crrev.com/0dd889e0cb36c81e872ffc768e471cb52a7f16f6/components/download/internal/test/mock_download_service.cc
[add] https://crrev.com/0dd889e0cb36c81e872ffc768e471cb52a7f16f6/components/download/internal/test/mock_download_service.h
[add] https://crrev.com/0dd889e0cb36c81e872ffc768e471cb52a7f16f6/components/download/internal/test/test_download_service.cc
[add] https://crrev.com/0dd889e0cb36c81e872ffc768e471cb52a7f16f6/components/download/internal/test/test_download_service.h